Uniform efficient light diffusing fiber

ABSTRACT

Light diffusing optical fibers for use illumination applications and which have a uniform color gradient that is angularly independent are disclosed herein along with methods for making such fibers. The light diffusing fibers are composed of a silica-based glass core that is coated with a number of layers including a scattering layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 USC §119 of U.S. application Ser. No. 14/577,437 filed on Dec.19, 2014, which is a continuation of U.S. application Ser. No.13/713,248 filed on Dec. 13, 2012 and claims the benefit of priority ofU.S. Provisional Application Ser. No. 61/577,159 filed Dec. 19, 2011,the contents of which are relied upon and incorporated herein byreference in their entirety.

FIELD

The present specification generally related to light diffusing opticalfibers for use in illumination applications, and, more specifically, tolight diffusing optical fibers which have a uniform color gradient thatis angularly independent and are usable for efficiently diffusing lightin the ultraviolet spectrum. Methods for making such fibers are alsodisclosed herein.

BACKGROUND

It has been found that optical fibers that allow for propagation oflight radially outwards along the length of the fiber, therebyilluminating the fiber, are particularly useful for a number ofapplications, such as special lighting, photochemistry, and for use inelectronics and display devices. However, there are a number of issueswith the current design of light diffusing fibers (“LDF”). One of theissues with the current design is that the angular distribution ofdifferent light colors from the fiber may vary depending on the viewingangle, especially for high lm/W cases, such as white LED, when bluelight from the light source is mixed with a down converting phosphor.Accordingly, there is a need for alternative light diffusing fiberdesigns that cure these deficiencies.

SUMMARY

A first embodiment comprises a light diffusing fiber for emittingultraviolet radiation comprising: a core comprising a silica-based glasscomprising scattering defects; a cladding in direct contact with thecore; and a scattering layer in direct contact with the cladding;wherein the intensity of the emitted ultraviolet radiation does not varyby more than about 30% for all viewing angle from about 10° to about170° relative to the direction of the light diffusing optical fiber. Insome embodiments the light diffusing optical fiber emits light having anintensity along the fiber that does not vary by more than about 20%. Insome embodiments, the scattering induced attenuation loss comprises fromabout 0.1 dB/m to about 50 dB/m at a wavelength from about 300 nm toabout 450 nm.

In some embodiments, the core comprises a plurality of randomlydistributed voids. In some embodiments, the cladding comprises apolymer. In some embodiments, the cladding comprises CPC6. In someembodiments, the scattering layer comprises a polymer. In someembodiments, the scattering layer comprises CPC6. In some embodiments,the scattering layer comprises nano- to microscale voids ormicroparticles or nanoparticles of a scattering material. In someembodiments, the microparticles or nanoparticles comprise SiO₂ or Zr.

In some embodiments, the light diffusing fiber further comprises a lightemitting device that emits light with a wavelength from about 300 nm toabout 450 nm into the core of the light diffusing fiber. In someembodiments, the light diffusing fiber further comprises a secondarylayer in between the cladding and scattering layer.

Another embodiment comprises a method of producing a light diffusingfiber comprising: forming an optical fiber preform comprising a preformcore; drawing the optical fiber preform into an optical fiber; coatingthe optical fiber with at least one cladding layer; and coating theoptical fiber with at least one scattering layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B describe a LDF embodiment (100) with a modified coatingfor uniform scattering (130) along with a phosphor layer (140) for whitecolor generation in both cross-section (FIG. 1A) and parallel section(FIG. 1B).

FIGS. 2A and 2B describe a LDF embodiment (200) with a coating modifiedfor uniform scattering of UV light using a scattering layer (230) incombination with a core (210) and cladding (220) case when coating ishigh absorbance at wavelength of the source.

FIG. 3A-D are spectra of different embodiments as a function of angle.FIG. 3A shows the output from a 160 μm thick polymer coating comprising35% by weight CeYAG (no scattering layer); FIG. 3B shows the output froma 800 μm thick polymer coating comprising 35% by weight CeYAG with noscattering layer; FIG. 3C shows the output from a 160 μm thick polymercoating comprising 20% by weight CeYAG with no scattering layer; andFIG. 3D shows the output from TiO₂ scattering layer (5 μm thick) and a160 μm thick polymer coating comprising 35% by weight CeYAG layer.

FIG. 4 shows the angular dependence of color coordinates (based on CIE1931 x, y chromaticity space) for a white LDF embodiment (shown in FIG.3D) as compared to data for a white LED and CCFL.

FIG. 5 describes the luminance per area comparison for a white LED strip(backlight for LG display), a CCFL for LG backlight illumination, and awhite LDF embodiment (as in FIG. 3D and FIG. 4) with a 200 mW source,and the white LDF (as in FIG. 3D and FIG. 4) embodiment output using2×1.5 W 445 laser diodes. The LDF was illuminated from both sides using50% MM coupler. Use of two compact 445 nm laser sources places thecurrent approximately 1 m long white LDF on the same luminance level asa standard CCFL.

FIG. 6 is comparison of spectra of white LED, CCFL and white LDFembodiment.

FIG. 7 is a diagram of the CIE 1931 x, y chromaticity space showing thechromacities of black-body light sources of various temperatures andlines of constant correlated color temperature.

FIG. 8 shows the angular dependence of light scattering for an UVdiffusing LDF embodiment with standard cladding of CPC6.

FIG. 9 shows the angular dependence of light scattering for UV diffusingLDF embodiment with a cladding of CPC6 and a scattering layer of CPC6(100 μm) doped with 2 microns spherical silica particles.

FIG. 10 is an image of white color LDF (FIG. 3D) comprising a scatteringlayer and a CeYAG-doped phosphor layer.

DETAILED DESCRIPTION

The present disclosure is provided as an enabling teaching and can beunderstood more readily by reference to the following description,drawings, examples, and claims. To this end, those skilled in therelevant art will recognize and appreciate that many changes can be madeto the various aspects of the embodiments described herein, while stillobtaining the beneficial results. It will also be apparent that some ofthe desired benefits of the present embodiments can be obtained byselecting some of the features without utilizing other features.Accordingly, those who work in the art will recognize that manymodifications and adaptations are possible and can even be desirable incertain circumstances and are a part of the present disclosure.Therefore, it is to be understood that this disclosure is not limited tothe specific compositions, articles, devices, and methods disclosedunless otherwise specified. It is also to be understood that theterminology used herein is for the purpose of describing particularaspects only and is not intended to be limiting.

Disclosed are materials, compounds, compositions, and components thatcan be used for, can be used in conjunction with, can be used inpreparation for, or are embodiments of the disclosed method andcompositions. These and other materials are disclosed herein, and it isunderstood that when combinations, subsets, interactions, groups, etc.of these materials are disclosed that while specific reference of eachvarious individual and collective combinations and permutation of thesecompounds may not be explicitly disclosed, each is specificallycontemplated and described herein. Thus, if a class of substituents A,B, and/or C are disclosed as well as a class of substituents D, E,and/or F, and an example of a combination embodiment, A-D is disclosed,then each is individually and collectively contemplated. Thus, in thisexample, each of the combinations A-E, A-F, B-D, B-E, B-F, C-D, C-E, andC-F are specifically contemplated and should be considered disclosedfrom disclosure of A, B, and/or C; D, E, and/or F; and the examplecombination A-D. Likewise, any subset or combination of these is alsospecifically contemplated and disclosed. Thus, for example, thesub-group of A-E, B-F, and C-E are specifically contemplated and shouldbe considered disclosed from disclosure of A, B, and/or C; D, E, and/orF; and the example combination A-D. This concept applies to all aspectsof this disclosure including, but not limited to any components of thecompositions and steps in methods of making and using the disclosedcompositions. Thus, if there are a variety of additional steps that canbe performed it is understood that each of these additional steps can beperformed with any specific embodiment or combination of embodiments ofthe disclosed methods, and that each such combination is specificallycontemplated and should be considered disclosed.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the followingmeanings:

“Include,” “includes,” or like terms means encompassing but not limitedto, that is, inclusive and not exclusive.

The term “about” references all terms in the range unless otherwisestated. For example, about 1, 2, or 3 is equivalent to about 1, about 2,or about 3, and further comprises from about 1-3, from about 1-2, andfrom about 2-3. Specific and preferred values disclosed forcompositions, components, ingredients, additives, and like aspects, andranges thereof, are for illustration only; they do not exclude otherdefined values or other values within defined ranges. The compositionsand methods of the disclosure include those having any value or anycombination of the values, specific values, more specific values, andpreferred values described herein.

The indefinite article “a” or “an” and its corresponding definitearticle “the” as used herein means at least one, or one or more, unlessspecified otherwise.

White Light Fibers

In light diffusing fibers, the dominant component of scattering is atlow angles, close to 5-10 degrees, (referencing angle 170 in FIG. 1B orangle 270 in FIG. 2B). Therefore, when yellow light from a phosphor(typically in a coating) is mixed with blue incident light, theresulting color depends on viewing angle. That is because yellow lightdue to phosphor emission is almost uniform in angular space (independentof angle 170) while the blue light has a strong low angle component(even after scattering). These two facts result in a color asymmetry,with low viewing angles having a dominant blue color and angles greaterthan 90 degrees have mostly yellow color. Embodiments solve theseproblems by homogenizing the scattered light in light diffusing fibersto provide light uniform in color as a function of viewing angle.

A first aspect comprises a light diffusing fiber comprising a layer ofscattering particles to obtain uniform color output as a function ofviewing angle. The desire is to produce a uniform white color outputfrom the light diffusing fiber. Such fibers could be used as replacementfor CCFL used in LCD backlight units, but have the additional advantageof being much thinner and therefore could be used with thinnerilluminating substrates.

Referring now to FIGS. 1A and 1B, one embodiment of a light diffusingoptical fiber 100 is schematically depicted. The light diffusing opticalfiber 100 generally comprises a core 110, which further comprises ascattering region. The scattering region may comprise gas filled voids,such as shown in U.S. application Ser. Nos. 12/950,045, 13/097,208, and13/269,055, herein incorporated by reference, or may comprise theinclusion of particles, such as micro- or nanoparticles of ceramicmaterials, into the fiber core.

The gas filled voids may occur throughout the core, may occur near theinterface of the core and cladding 120, or may occur as an annular ringwithin the core. The gas filled voids may be arranged in a random ororganized pattern and may run parallel to the length of the fiber or maybe helical (i.e., rotating along the long axis of the fiber). Thescattering region may comprise a large number of gas filled voids, forexample more than 50, more than 100, or more than 200 voids in the crosssection of the fiber. The gas filled voids may contain, for example,SO₂, Kr, Ar, CO₂, N₂, O₂, or mixtures thereof. The cross-sectional size(e.g., diameter) of the voids may be from about 10 nm to about 10 μm andthe length may vary from about 1 μm to about 50 m. In some embodiments,the cross sectional size of the voids is about 10 nm, 20 nm, 30 nm, 40nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm,180 nm, 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm,1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. In someembodiments, the length of the voids is about 1 μm, 2 μm, 3 μm, 4 μm, 5μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700μm, 800 μm, 900 μm, 1000 μm, 5 mm, 10 mm, 50 mm, 100 mm, 500 mm, 1 m, 5m, 10 m, 20 m, or 50 m.

In the embodiment shown in FIGS. 1A and 1B, the core portion 110comprises silica-based glass and has an index of refraction, n. In someembodiments, the index of refraction for the core is about 1.458. Thecore portion 110 may have a radius of from about 10 μm to about 600 μm.In some embodiment the radius of the core is from about 30 μm to about400 μm. In other embodiments, the radius of the core is about 125 μm toabout 300 μm. In still other embodiments, the radius of the core isabout 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 140 μm, 160 μm,180 μm, 200 μm, 220 μm, 240 μm, or 250 μm.

The voids in the core 110 are utilized to scatter light propagating inthe core of the light diffusing optical fiber 100 such that the light isdirected radially outward from the core portion 110, therebyilluminating the light diffusing optical fiber and the space surroundingthe light diffusing optical fiber. The scatter-induced attenuation maybe increased through increasing the concentration of voids, positioningvoids throughout the fiber, or in cases where the voids are limited toan annular ring, increasing the width of the annulus comprising thevoids will also increase the scattering-induced attenuation for the samedensity of voids. Additionally, in compositions where the voids arehelical, the scattering-induced attenuation may also be increased byvarying the pitch of the helical voids over the length of the fiber.Specifically, it has been found that helical voids with a smaller pitchscatter more light than helical voids with a larger pitch. Accordingly,the intensity of the illumination of the fiber along its axial lengthcan be controlled (i.e., predetermined) by varying the pitch of thehelical voids along the axial length. The pitch of the helical voids, asused herein, refers to the inverse of the number times the helical voidsare wrapped or rotated around the long axis of the fiber per unitlength.

Still referring to FIGS. 1A and 1B, the light diffusing optical fiber100 may further comprise a cladding 120 which surrounds and is in directcontact with the core portion 110. The cladding 120 may be formed from amaterial which has a low refractive index in order to increase thenumerical aperture (NA) of the light diffusing optical fiber 100. Insome embodiments, the cladding has a refractive index contrast (ascompared to the core) of less than about 1.415. For example, thenumerical aperture of the fiber may be greater than about 0.3, and insome embodiments greater than about 0.4. In one embodiment, the cladding120 comprises a low index polymeric material such as UV or thermallycurable fluoroacrylate, such as PC452 available from SSCP Co. Ltd 403-2,Moknae, Ansan, Kyunggi, Korea, or silicone. In other embodiments, thecladding comprises a urethane acrylate, such as CPC6, manufactured byDSM Desotech, Elgin, Ill. In still other embodiments the cladding 120comprises a silica glass which is down-doped with a down-dopant, suchas, for example, fluorine. In some embodiments, the cladding comprises ahigh modulus coating. The cladding 120 generally has an index ofrefraction which is less than the index of refraction of the coreportion 110. In some embodiments, the cladding 120 is a low indexpolymer cladding with a relative refractive index that is negativerelative to silica glass. For example, the relative refractive index ofthe cladding may be less than about −0.5% and in some embodiments lessthan −1%.

The cladding 120 generally extends from the outer radius of the coreportion 110. In some embodiments described herein, the radial width ofthe cladding is greater than about 10 μm, greater than about 20 μm,greater than about 50 μm or greater than about 70 μm. In someembodiments, the cladding has a thickness of about 10 μm, 20 μm, 30 μm,40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.

The light diffusing fiber may also comprise a clear layer of secondarycoating typical for all optical fibers for mechanical handling. Thescattering layer will be on top of the secondary coating. In someembodiments the secondary coating layer and scattering layer may becombined, depending on how fiber is manufactured. For example, if thescattering layer is applied after initial draw of the fiber, forhandling issues it may be necessary to apply a clear secondary coatingwith a second step being directed to application of the scattering layerand phosphor. This process is similar to postdraw ink application foroptical fibers. However, it can be combined in one step in the draw, andin this case secondary coating is not needed and the scattering layermay be applied directly on top of the cladding.

Referring again to FIGS. 1A and 1B, the light diffusing optical fiber100 further comprises a scattering layer 130 which surrounds and is indirect contact with the cladding 120. The scattering layer may comprisea polymer coating. The polymer coating may comprise be any liquidpolymer or prepolymer material into which the scattering agent could beadded and in which the blend may be applied to the fiber as a liquid andthen converted to a solid after application to the fiber. In someembodiments, the scattering layer 130 comprises a polymer coating suchas an acrylate-based, such as CPC6, manufactured by DSM Desotech, Elgin,Ill., or silicone-based polymer further comprising a scatteringmaterial. In another embodiment, the cladding 120 comprises a low indexpolymeric material such as UV or thermally curable fluoroacrylate, suchas PC452 available from SSCP Co. Ltd 403-2, Moknae, Ansan, Kyunggi,Korea. In some embodiments, the cladding comprises a high moduluscoating. In some embodiments, it was most efficient to blend thescattering agents into standard UV curable acrylate based optical fibercoatings, such as Corning's standard CPC6 secondary optical fibercoating. To make the scattering blends, a concentrate was first made bymixing 30% by weight of the scattering agent into DSM 950-111 secondaryCPC6 optical fiber coating and then passing the mix over a 3 roll mill.These concentrates were then either applied directly as coatings or werefurther diluted with DSM 950-111 to give the desired scattering effect.In at least some embodiments, the coating layer 110 has a constantdiameter along the length of the light diffusing optical fiber.

In some embodiments, the scattering layer 130 may be utilized to enhancethe distribution and/or the nature of the light emitted radially fromthe core portion 110 and passed through the cladding 120. The scatteringmaterial may comprise nano- or microparticles with an average diameterof from about 200 nm to about 10 μm. In some embodiments, the averagediameter of the particles is about 200 nm, 300 nm, 400 nm, 500 nm, 600nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8μm, 9 μm, or 10 μm. The concentration of the scattering particles mayvary along the length of the fiber or may be constant and may be aweight percent sufficient to provide even scattering of the light whilelimiting overall attenuation. In some embodiments, the weight percentageof the scattering particles in the scattering layer comprises about 1%,2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%,18%, 19%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%. In some embodiments, thescattering layer comprises small particles of a scattering materialwhich comprise a metal oxides or other high refractive index material,such as TiO₂, ZnO, SiO₂, or Zr. The scattering material may alsocomprise micro- or nanosized particles or voids of law refractive index,such as gas bubbles. The scattering layer generally extends from theouter radius of the cladding 120. In some embodiments described herein,the radial width of the scattering layer is greater than about 1 μm, 2μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.

In some embodiments, the scattering material may contain TiO₂-basedparticles, such as a white ink, which provides for an angle independentdistribution of light scattered from the core portion 110 of the lightdiffusing optical fiber 100. In some embodiments, the scatteringparticles comprise a sublayer within the scattering layer. For example,in some embodiments, the particle sublayer may have a thickness of about1 μm to about 5 μm. In other embodiments, the thickness of the particlelayer and/or the concentration of the particles in the scattering layermay be varied along the axial length of the fiber so as to provide moreuniform variation in the intensity of light scattered from the lightdiffusing optical fiber 100 at large angles (i.e., angles greater thanabout 15 degrees).

Referring again to FIGS. 1A and 1B, the light diffusing optical fiber100 further comprises a phosphor layer 140 which surrounds and is indirect contact with the scattering layer 130. The fluorescent orphosphorescent material in the phosphor layer may comprise any organicor inorganic fluorescent or phosphorescent material, and in someembodiments may be an inorganic material. For example, the phosphorlayer may comprise CeYAG, NdYAG, quantum dots, nanoparticles,metal-enhanced fluorescence of organic fluorophores, etc.

The phosphor layer may comprise a polymer coating. The polymer coatingmay comprise be any liquid polymer or prepolymer material into which thefluorescent or phosphorescent material could be added and in which theblend may be applied to the fiber as a liquid and then converted to asolid after application to the fiber. For example, in one embodiment,the phosphor layer 140 comprises a polymer coating such as anacrylate-based or silicone based polymer (e.g., CPC6 secondary coating)further comprising a fluorescent or phosphorescent material thatconverts light scattered from the core portion 110 to a longerwavelength of light. In some embodiments, it was most efficient to blendthe fluorescent or phosphorescent material into standard UV curableacrylate based optical fiber coatings, such as Corning's standard CPC6secondary optical fiber coating. To make the fluorescent orphosphorescent blend, a concentrate was first made by mixing 30% byweight of the fluorescent or phosphorescent agent into DSM 950-111secondary CPC6 optical fiber coating and then passing the mix over a 3roll mill. These concentrates were then either applied directly ascoatings or were further diluted with DSM 950-111 to give the desiredfluorescent or phosphorescent effect.

In some embodiments, white light can be emitted from the light diffusingoptical fiber by coupling the light diffusing optical fiber 100 with afluorescent or phosphorescent material in the phosphor layer 140 to ahigher energy (lower wavelength) light source, such as a UV or near UVlight source emitting at 405 nm or 445 nm. In such an embodiments, thediode laser. The UV light from the light source that is scattered fromthe core portion 110 causes the material in the phosphor layer tofluoresce or phosphoresce such that the combination of UV light andemitted wavelengths produce a white light emission from the lightdiffusing optical fiber 100. In some embodiments, the source light isfrom about 300-550 nm, or about 300, 350, 400, 450, 500, or 550 nm.

Referring to FIG. 1B, in the embodiment shown, unscattered lightpropagates down the light diffusing fiber 100 from the source in thedirection shown by arrow 150. Scattered light is shown exiting the lightdiffusing fiber as arrow 160 at an angle 170, which describes angulardifference between the direction of the fiber and the direction of thescattered light when it leaves light diffusing fiber 100. In someembodiments, the UV-visible spectrum of the light diffusing fiber 100 isindependent of angle 170. In some embodiments, the intensities of thespectra when angle 170 is 15° and 150° are within ±30% as measured atthe peak wavelength. In some embodiments, the intensities of the spectrawhen angle 170 is 15° and 150° are within ±20%, ±15%, ±10%, or ±5% asmeasured at the peak wavelength.

In some embodiments, the output of the light diffusing fiber comprises acombination of the scattered incident UV light and the scatteredfluorescent or phosphorescent light from the phosphor material toproduce a combined light that has the optical property of appearingwhite. In some embodiments, the combined light has an x coordinate fromabout 0.15 to about 0.25 and y coordinate of from about 0.20 to about0.30 when measured on the x- and y-axes of the CIE 1931 x, y chromacityspace (T. Smith and J. Guild, The C.I.E. Colorimetric Standards andTheir Use, 33 TRANS. OP. Soc. 73-134 (1931) herein incorporated byreference in its entirety) (see FIG. 7). In some embodiments, thecombined light has an x coordinate from about 0.18 to about 0.23, orabout 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, or0.25 on the CIE 1931 x, y chromacity space. In some embodiments, thecombined light has a y coordinate from about 0.23 to about 0.27, orabout 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, or0.30 on the CIE 1931 x, y chromacity space.

In some embodiments, the values of the x and y coordinates of the CIE1931 x, y chromacity space do not vary more than ±30% with angle 170when angle 170 is from about 10° to about 170°. In some embodiments, thevalues of the x and y coordinates of the CIE 1931 x, y chromacity spaceat angles 170 of 15° and 150° are within ±30%, ±25%, ±20%, ±15%, ±10%,or ±5% of each other.

In some embodiments described herein the light diffusing optical fiberswill generally have a length from about 100 m to about 0.15 m. In someembodiments, the light diffusing optical fibers will generally have alength of about 100 m, 75 m, 50 m, 40 m, 30 m, 20 m, 10 m, 9 m, 8 m, 7m, 6 m, 5 m, 4 m, 3 m, 2 m, 1 m, 0.75 m, 0.5 m, 0.25 m, 0.15 m, or 0.1m.

Further, the light diffusing optical fibers described herein have ascattering induced attenuation loss of greater than about 0.2 dB/m at awavelength of 550 nm. For example, in some embodiments, the scatteringinduced attenuation loss may be greater than about 0.5 dB/m, 0.6 dB/m,0.7 dB/m, 0.8 dB/m, 0.9 dB/m, 1 dB/m, 1.2 dB/m, 1.4 dB/m, 1.6 dB/m, 1.8dB/m, 2.0 dB/m, 2.5 dB/m, 3.0 dB/m, 3.5 dB/m, or 4 dB/m, 5 dB/m, 6 dB/m,7 dB/m, 8 dB/m, 9 dB/m, 10 dB/m, 20 dB/m, 30 dB/m, 40 dB/m, or 50 dB/mat 550 nm.

As described herein, the light diffusing fiber can be constructed toproduce uniform illumination along the entire length of the fiber oruniform illumination along a segment of the fiber which is less than theentire length of the fiber. The phrase “uniform illumination,” as usedherein, means that the intensity of light emitted from the lightdiffusing fiber does not vary by more than 25% over the specifiedlength.

The fibers described herein may be formed utilizing various techniques.For example, the core 110 can be made by any number of methods whichincorporate voids or particles into the glass fiber. For example,methods for forming an optical fiber preform with voids are describedin, for example, U.S. patent application Ser. No. 11/583,098, which isincorporated herein by reference. Additional methods of forming voidsmay be found in, for example, U.S. application Ser. Nos. 12/950,045,13/097,208, and 13/269,055, herein incorporated by reference. Generally,the optical fiber is drawn from an optical fiber preform with a fibertake-up system and exits the draw furnace along a substantially verticalpathway. In some embodiments, the fiber is rotated as it drawn toproduce helical voids along the long axis of the fiber. As the opticalfiber exits the draw furnace, a non-contact flaw detector may be used toexamine the optical fiber for damage and/or flaws that may have occurredduring the manufacture of the optical fiber. Thereafter, the diameter ofthe optical fiber may be measured with non-contact sensor. As theoptical fiber is drawn along the vertical pathway, the optical fiber mayoptionally be drawn through a cooling system which cools the opticalfiber prior to the coatings being applied to the optical fiber.

After the optical fiber exits the draw furnace or optional coolingsystem, the optical fiber enters at least one coating system where oneor more polymer layers (i.e., the polymeric cladding material, thescattering layer, and/or the phosphor layer) are applied to the opticalfiber. As the optical fiber exits the coating system, the diameter ofthe optical fiber may be measured with non-contact sensor. Thereafter, anon-contact flaw detector is used to examine the optical fiber fordamage and/or flaws in the coating that may have occurred during themanufacture of the optical fiber.

UV Fibers

Another aspect comprises a light diffusing fiber with high efficienciesof light extraction at wavelengths where the fiber cladding has highabsorptions, such as below 450 nm. Using LDF for UV wavelengths helps toextend the range of applications for photoreactors, water/airpurification, acrylate polymerizations and related. Popular desiredwavelengths that are used for photoreactions (i.e. less than about 400nm) and typical UV curable polymers have strong absorptions at thiswavelength due to the need for photo-initiators. Embodiments hereinimprove the efficiency of the light extraction from LDF, which isnormally trapped in the high index secondary coating. One notable use ofthe LDF fiber at this wavelength would be the ability to place light inremote, small, and difficult to access locations for curing UVmaterials.

In a first aspect, scattering centers (transparent at wavelengths lessthan about 400 nm), such as small silica particles, are added to thefiber as a scattering layer so that the light is scattered from thescattering coating without significant propagation. This allows for anefficient LDF even at wavelengths where the coating does absorb light.In some embodiments, the low index glass cladding may be replaced withlow index F/B co-doped glass cladding. This type of cladding doesn'tgive as high an NA as in the case of a low index polymer used as acladding, but is high enough for a wide range of applications.

Referring now to FIGS. 2A and 2B, one embodiment of a light diffusingoptical fiber 200 is schematically depicted. The light diffusing opticalfiber 200 generally comprises a core 210, which further comprises ascattering region. The scattering region may comprise gas filled voids,such as shown in U.S. application Ser. Nos. 12/950,045, 13/097,208, and13/269,055, herein incorporated by reference, or may comprise theinclusion of particles, such as micro- or nanoparticles, into the fibercore.

The gas filled voids may occur throughout the core, may occur near theinterface of the core and cladding 220, or may occur as an annular ringwithin the core. The gas filled voids may be arranged in a random ororganized pattern and may run parallel to the length of the fiber or maybe helical (i.e., rotating along the long axis of the fiber). Thescattering region may comprise a large number of gas filled voids, forexample more than 50, more than 100, or more than 200 voids in the crosssection of the fiber. The gas filled voids may contain, for example,SO₂, Kr, Ar, CO₂, N₂, O₂, or mixtures thereof. The cross-sectional size(e.g., diameter) of the voids may be from about 10 nm to about 10 μm andthe length may vary from about 1 μm to about 50 m. In some embodiments,the cross sectional size of the voids is about 10 nm, 20 nm, 30 nm, 40nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm,180 nm, 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm,1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. In someembodiments, the length of the voids is about 1 μm, 2 μm, 3 μm, 4 μm, 5μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700μm, 800 μm, 900 μm, 1000 μm, 5 mm, 10 mm, 50 mm, 100 mm, 500 mm, 1 m, 5m, 10 m, 20 m, or 50 m.

In the embodiment shown in FIGS. 2A and 2B, the core portion 210comprises silica-based glass and has an index of refraction, n. In someembodiments, the index of refraction for the core is about 1.458. Thecore portion 210 may have a radius of from about 10 μm to about 600 μm.In some embodiment the radius of the core is from about 30 μm to about400 μm. In other embodiments, the radius of the core is from about 125μm to about 300 μm. In still other embodiments, the radius of the coreis about 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 140 μm, 160μm, 180 μm, 200 μm, 220 μm, 240 μm, or 250 μm.

The voids in the core 210 are utilized to scatter light propagating inthe core of the light diffusing optical fiber 200 such that the light isdirected radially outward from the core portion 210, therebyilluminating the light diffusing optical fiber and the space surroundingthe light diffusing optical fiber. The scatter-induced attenuation maybe increased through increasing the concentration of voids, positioningvoids through out the fiber, or in cases where the voids are limited toan annular ring, increasing the width of the annulus comprising thevoids will also increase the scattering-induced attenuation for the samedensity of voids. Additionally, in compositions where the voids arehelical, the scattering-induced attenuation may also be increased byvarying the pitch of the helical voids over the length of the fiber.Specifically, it has been found that helical voids with a smaller pitchscatter more light than helical voids with a larger pitch. Accordingly,the intensity of the illumination of the fiber along its axial lengthcan be controlled (i.e., predetermined) by varying the pitch of thehelical voids along the axial length. The pitch of the helical voids, asused herein, refers to the inverse of the number times the helical voidsare wrapped or rotated around the long axis of the fiber per unitlength.

Still referring to FIGS. 2A and 2B, the light diffusing optical fiber200 may further comprise a cladding 220 which surrounds and is in directcontact with the core portion 210. In some embodiments, the claddingcomprises a fluorine and boron co-doped glass. In some embodiments, thecladding comprises a polymer. The cladding 220 may be formed from amaterial which has a low refractive index in order to increase thenumerical aperture (NA) of the light diffusing optical fiber 200. Insome embodiments, the cladding has a refractive index contrast (ascompared to the core) of less than about 1.415. For example, thenumerical aperture of the fiber may be greater than about 0.3, and insome embodiments, greater than about 0.4. In one embodiment, thecladding 220 comprises a low index polymeric material such as UV orthermally curable fluoroacrylate, such as PC452 available from SSCP Co.Ltd 403-2, Moknae, Ansan, Kyunggi, Korea, or silicone. In otherembodiments, the cladding comprises a urethane acrylate, such as CPC6,manufactured by DSM Desotech, Elgin, Ill. In other embodiments thecladding 220 may be formed from silica glass which is down-doped with adown-dopant, such as, for example, fluorine and boron. The cladding 220generally has an index of refraction which is less than the index ofrefraction of the core portion 210. In some embodiments, the cladding220 is a low index polymer cladding with a relative refractive indexthat is negative relative to silica glass. For example, the relativerefractive index of the cladding may be less than about −0.5% and insome embodiments less than −1%.

The cladding 220 generally extends from the outer radius of the coreportion 210. In some embodiments described herein, the radial width ofthe cladding is greater than about 10 μm, greater than about 20 μm,greater than about 50 μm or greater than about 70 μm. In someembodiments, the cladding has a thickness of about 10 μm, 20 μm, 30 μm,40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.

The light diffusing fiber may also comprise a clear layer of secondarycoating typical for mechanical handling. In the case of UV scatteringfibers, it is possible to minimize the thickness of any secondarycoatings that may absorb UV radiation. The scattering layer will be ontop of the secondary coating. In some embodiments the secondary coatinglayer and scattering layer may be combined, depending on how fiber ismanufactured. For example, if the scattering layer is applied afterinitial draw of the fiber, for handling issues it may be necessary toapply a clear secondary coating with a second step being directed toapplication of the scattering layer and phosphor. This process issimilar to postdraw ink application for optical fibers. However, it canbe combined in one step in the draw, and in this case secondary coatingis not needed and the scattering layer may be applied directly on top ofthe cladding.

Referring again to FIGS. 2A and 2B, the light diffusing optical fiber200 further comprises a scattering layer 230 which surrounds and is indirect contact with the cladding 220. For example, in one embodiment,the scattering layer 230 comprises a polymer coating such as anacrylate-based or silicone based polymer further comprising a scatteringmaterial. In at least some embodiments, the coating layer 210 has aconstant diameter along the length of the light diffusing optical fiber.

In some embodiments, the scattering layer 230 may be utilized to enhancethe distribution and/or the nature of the light emitted radially fromthe core portion 210 and passed through the cladding 220. The scatteringlayer may comprise a polymer coating. The polymer coating may comprisebe any liquid polymer or prepolymer material into which the scatteringagent could be added and in which the blend may be applied to the fiberas a liquid and then converted to a solid after application to thefiber. In some embodiments, the scattering layer 230 comprises a polymercoating such as an acrylate-based, such as CPC6, manufactured by DSMDesotech, Elgin, Ill., or silicone-based polymer further comprising ascattering material. In another embodiment, the cladding 220 comprises alow index polymeric material such as UV or thermally curablefluoroacrylate, such as PC452 available from SSCP Co. Ltd 403-2, Moknae,Ansan, Kyunggi, Korea. In some embodiments, the cladding comprises ahigh modulus coating. In some embodiments, it was most efficient toblend the scattering agents into standard UV curable acrylate basedoptical fiber coatings, such as Corning's standard CPC6 secondaryoptical fiber coating. To make the scattering blends, a concentrate wasfirst made by mixing 30% by weight of the scattering agent into DSM950-111 secondary CPC6 optical fiber coating and then passing the mixover a 3 roll mill. These concentrates were then either applied directlyas coatings or were further diluted with DSM 950-111 to give the desiredscattering effect.

In some embodiments, the scattering layer 230 may be utilized to enhancethe distribution and/or the nature of the light emitted radially fromthe core portion 210 and passed through the cladding 220. The scatteringmaterial may comprise nano- or microparticles with an average diameterof from about 200 nm to about 10 μm. In some embodiments, the averagediameter of the particles is about 200 nm, 300 nm, 400 nm, 500 nm, 600nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8μm, 9 μm, or 10 μm. The concentration of the scattering particles mayvary along the length of the fiber or may be constant and may be aweight percent sufficient to provide even scattering of the light whilelimiting overall attenuation. In some embodiments, the weight percentageof the scattering particles comprises about 1%, 2%, 3%, 4%, 5%, 6%, 7%,8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 25%, 30%,35%, 40%, 45%, or 50%. In some embodiments, the scattering layercomprises a scattering material that is not significantly absorbent inthe UV region of incident beam. In some embodiments the scatteringmaterial comprises metal oxides or other materials with low absorbancein the region from about 350 nm to about 420 nm, such as SiO₂ or Zr, ormay comprise nano- to microscale voids comprising a gas, such as oxygen,nitrogen, or a noble gas. The scattering layer generally extends fromthe outer radius of the cladding 220. In some embodiments describedherein, the radial width of the scattering layer is greater than about10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100μm.

In some embodiments, the scattering material may contain SiO₂-basedparticles, which provides for an angle independent distribution of lightscattered from the core portion 210 of the light diffusing optical fiber200. In some embodiments, the particles comprise a layer within thescattering layer. For example, in some embodiments, the particle layermay have a thickness of about 1 μm to about 5 μm. In other embodiments,the thickness of the scattering layer may be varied along the axiallength of the fiber so as to provide more uniform variation in theintensity of light scattered from the light diffusing optical fiber 200at large angles (i.e., angles greater than about 15 degrees).

Referring to FIG. 2B, in the embodiment shown, unscattered lightpropagates down the light diffusing fiber 200 from the source in thedirection shown by arrow 250. Scattered light is shown exiting the lightdiffusing fiber as arrow 260 at an angle 270, which describes angulardifference between the direction of the fiber and the direction of thescattered light when it leaves light diffusing fiber 200. In someembodiments, the UV-visible spectrum of the light diffusing fiber 200 isindependent of angle 270. In some embodiments, the intensities of thespectra when angle 270 is 15° and 150° are within ±30% as measured atthe peak wavelength. In some embodiments, the intensities of the spectrawhen angle 270 is 15° and 150° are within ±20%, ±15%, ±10%, or ±5% asmeasured at the peak wavelength.

In some embodiments described herein the light diffusing optical fiberswill generally have a length from about 100 m to about 0.15 m. In someembodiments, the light diffusing optical fibers will generally have alength of about 100 m, 75 m, 50 m, 40 m, 30 m, 20 m, 10 m, 9 m, 8 m, 7m, 6 m, 5 m, 4 m, 3 m, 2 m, 1 m, 0.75 m, 0.5 m, 0.25 m, 0.15 m, or 0.1m.

Further, the light diffusing optical fibers described herein have ascattering induced attenuation loss of greater than about 0.2 dB/m at awavelength of 300 nm, 325 nm, 350 nm, 375 nm, 400 nm, 425 nm, or 450 nm.For example, in some embodiments, the scattering induced attenuationloss may be greater than about 0.5 dB/m, 0.6 dB/m, 0.7 dB/m, 0.8 dB/m,0.9 dB/m, 1 dB/m, 1.2 dB/m, 1.4 dB/m, 1.6 dB/m, 1.8 dB/m, 2.0 dB/m, 2.5dB/m, 3.0 dB/m, 3.5 dB/m, 4 dB/m, 5 dB/m, 6 dB/m, 7 dB/m, 8 dB/m, 9dB/m, 10 dB/m, 20 dB/m, 30 dB/m, 40 dB/m, or 50 dB/m at 300 nm, 325 nm,350 nm, 375 nm, 400 nm, 425 nm, or 450 nm.

As described herein, the light diffusing fiber may be constructed toproduce uniform illumination along the entire length of the fiber oruniform illumination along a segment of the fiber which is less than theentire length of the fiber. The phrase “uniform illumination,” as usedherein, means that the intensity of light emitted from the lightdiffusing fiber does not vary by more than 25% over the specifiedlength.

The fibers described herein may be formed utilizing various techniques.For example, the core 210 can be made by any number of methods whichincorporate voids are particles into the glass fiber. For example,methods for forming an optical fiber preform with voids are describedin, for example, U.S. patent application Ser. No. 11/583,098, which isincorporated herein by reference. Additional methods of forming voidsmay be found in, for example, U.S. application Ser. Nos. 12/950,045,13/097,208, and 13/269,055, herein incorporated by reference. Generally,the optical fiber is drawn from an optical fiber preform with a fibertake-up system and exits the draw furnace along a substantially verticalpathway. In some embodiments, the fiber is rotated as it drawn toproduce helical voids along the long axis of the fiber. As the opticalfiber exits the draw furnace, a non-contact flaw detector may be used toexamine the optical fiber for damage and/or flaws that may have occurredduring the manufacture of the optical fiber. Thereafter, the diameter ofthe optical fiber may be measured with non-contact sensor. As theoptical fiber is drawn along the vertical pathway, the optical fiber mayoptionally be drawn through a cooling system which cools the opticalfiber prior to the coatings being applied to the optical fiber.

After the optical fiber exits the draw furnace or optional coolingsystem, the optical fiber enters at least one coating system where oneor more polymer layers (i.e., the polymeric cladding material and/or thescattering layer) are applied to the optical fiber. As the optical fiberexits the coating system, the diameter of the optical fiber may bemeasured with non-contact sensor. Thereafter, a non-contact flawdetector is used to examine the optical fiber for damage and/or flaws inthe coating that may have occurred during the manufacture of the opticalfiber.

Examples

In order to efficiently make samples a mini-recoat tower was assembled.This small tower has the advantage that any existing fiber can beover-coated offline with a layer of UV curable coating. The cure wasaccomplished by the use of a 200 W Hg-lamp and draw speed of ˜0.1 m/s.Three options were tested to provide uniform angular distribution of thescattering light from the fiber:

Option 1—A fiber comprising a silica core, a polymer cladding, ascattering layer, and a phosphor layer. The scattering layer comprisedsilica particles in a polymer and the phosphor layer comprised CeYAG ina polymer. The refractive index of the polymer cladding was 1.55, andsilica was ˜1.46, so with the significant index mismatch and small sizeof silica particles (˜1 μm), it was posited that it may be possible toachieve uniform scattering diagram as a function of angle relative toincident angle.

Option 2—A fiber comprising a silica core, a polymer cladding, and asingle layer comprising both the phosphor layer and the scatteringmedium. CeYAG particles have a refractive index of about 1.8, and assuch have a significant mismatch with polymer cladding (˜1.55). Butsince CeYAG the particles used were large (˜3-4 μm), it was assumed thatthey would not produce significant scattering.

Option 3—A fiber comprising a silica core, a polymer cladding, ascattering layer, and a phosphor layer. The scattering layer uses highefficient scatterers, such as white ink (TiO₂ based filled polymer).TiO₂ has high refractive index (˜2.5), so it may be a more efficientscatterer than SiO₂ particles. However, TiO₂ absorbs light atwavelength<400 nm and is less suitable for UV light applications.

In each case the thickness of each layer and concentration of thedopants was modified to obtain optimum spectrum and angular dependence.In FIGS. 1A and 1B are shown a scattering layer and layer doped withphosphor particles. This design was used for white color fibers. InFIGS. 2A and 2B are shown a fiber design for UV emission with asecondary coating doped with scattering particles for uniform angulardependence.

The scattering emission spectra of various fibers are shown in FIGS.3A-3D. The incident light had a wavelength of 445 nm and the silicafiber used was a random airline fiber. As can be seen in FIGS. 3A-3C, a160 um-thick single layer of 35 wt. % CeYAG with no scattering material(FIG. 3A), a 800 um-thick single layer of 35 wt. % CeYAG with noscattering material (FIG. 3B), and a 160 um-thick single layer of 20 wt.% CeYAG with no scattering material (FIG. 3C) all failed to providesufficient scattering to over come the angular dependence of lightcolor, i.e., the color of the emitted light appeared more blue as angle170 of FIG. 1 approached 0°. Additionally, it was found that changingthe diameter and amount of CeYAG in the phosphor layer showed thatspectrum of scattered light changes very strongly as function of viewingangle and the amount of CeYAG present.

FIG. 3D shows a number of spectra arising from a fiber comprising ascattering layer comprising TiO₂ particles (4 μm-thick layer) plus a 160μm-thick layer of 35 wt. % CeYAG as a function of angle. As can be seenfrom the spectra, the combination of a scattering layer and phosphorlayer provides light emission from the fiber that is independent ofviewing angle.

FIG. 4 shows a color coordinated comparison using CIE 1931 x, ychromaticity space values for an embodiment (comprising a silica core,polymer cladding, scattering layer (4 μm-thick layer of TiO₂) andphosphor layer (160 μm-thick layer of 35 wt. % CeYAG)) is compared to awhite LED (which also uses CeYAG in combination with a 460 nm blue LEDto obtain white light) and CCFL. The color coordinates of the lightdiffusing fiber place the color output well within the region of what isconsidered white light (see FIG. 7). Further, as can be seen from thechart, the color is independent of viewing angle.

Theoretical projections of the fiber brightness (FIG. 5) show that itwould be possible to reach the same brightness as CCFL for liquidcrystal displays using two laser diodes with 1.5 W power, which arecommercially available for very low costs.

Different amounts of scattering particles and CeYAG particles were usedin order to provide the right combination of scattering and absorptionof 445 nm light, while still allowing sufficient non-absorbed 445 nmlight provides the necessary blue color to make white light. The bestresults were obtained using about 35% by weight CeYAG and thicknesses ofabout 160 p.m. Additionally, this amount gave reasonable viscosity tothe secondary coating so it can be applied in a regular way to fiber indraw tower. It was also found that by bringing light in from two sidesof the LDF, it was possible to obtain more even uniform illuminationboth angularly and along the length of the fiber (FIG. 11).

For UV applications, silica micro-spheres were placed in the secondarycoating. The results show that the angular distribution can changesignificantly (FIGS. 8 and 9). FIG. 8 shows a light diffusing fibercomprising a random airline core and a standard polymer cladding. As canbe seen from the spectrum, the majority of the light is being emittedfrom the end of the fiber and very little UV light is being scattered.FIG. 9 shows the spectrum of an embodiment of the light diffusing fiber.The fiber in FIG. 9 comprises a random airline silica core, a polymercladding and a scattering layer comprising SiO₂ particles with ascattering loss of ˜3 dB/m. As can be seen in FIG. 9, the light isbroadly scattered and almost no light is being transmitted out of theend of the fiber. The large angle distribution shown in FIG. 9 isimportant for maximum distance coverage from surface of the fiber inapplication where photochemical reactions take place. Measurements forboth FIGS. 8 and 9 were done in media that matched the refraction indexof the fiber core. This means that in media with smaller refractiveindex, e.g. air, a lot of light from FIG. 8 would be trapped in the highindex secondary coating. However, if the scattering layer is present,even in air most of the light would escape from the secondary coatingvery efficiently. Therefore, doping of the secondary coating with silicaparticles both 1) scatters the light from the secondary coating and 2)also helps to reduce the refractive index of the secondary coatingthereby making trapping less efficient.

We claim:
 1. A light diffusing fiber capable of emitting light, saidfiber comprising: a core and a cladding such that for all viewing-anglesfrom about 40° to about 90° relative to the direction of propagation ofthe light in the light diffusing optical fiber the intensity of the ofthe emitted radiation does not vary by more than 42% of maximumintensity value.
 2. A light diffusing fiber comprising: a. a core and acladding; and b. nano- to microscale voids or nano or microparticles ofa scattering material, situated and distributed such that for allviewing-angles from about 40° to about 90° relative to the direction ofpropagation of the light in the light diffusing optical fiber theintensity of the of the emitted radiation does not vary by more than 42%of maximum intensity value.
 3. The light diffusing fiber of claim 1,wherein said core is a silica based core surrounded by a cladding. 4.The light diffusing fiber of claim 1, wherein a scattering layersurrounds the core, wherein at least said scattering layer comprises apolymer matrix with said nano- to microscale voids or nano ormicroparticles of said scattering material situated therein.
 5. Thelight diffusing fiber of claim 4, further comprising a claddingsurrounding said core, wherein a scattering layer surrounds the core andthe cladding, wherein said scattering layer comprises a polymer matrixwith said nano- to microscale voids or nano or microparticles of saidscattering material situated therein.
 6. The light diffusing fiber of 1,wherein maximum intensity value occurs at an angular position of at anangle of at least 42.5 degrees, relative to the direction of propagationof the light in the light diffusing optical fiber.
 7. The lightdiffusing fiber of claim 1, wherein said core is a silica based coresurrounded by a cladding.
 8. A light diffusing fiber comprising: a. acore comprising a silica-based glass comprising scattering defects; andb. a scattering layer surrounding the core, the scattering layercomprising nano- to microscale voids or nano or microparticles of ascattering material in a polymer matrix; such that when light ispropagating through the light diffusing fiber the intensity of theemitted radiation does not vary by more than about ±21% from averageintensity for viewing-angles between 40° and 90°, relative to thedirection of propagation of the light in the light diffusing opticalfiber.
 9. The light diffusing fiber of 8, wherein maximum intensityvalue occurs at an angular position of at an angle of at least 42.5degrees, relative to the direction of propagation of the light in thelight diffusing optical fiber.
 10. The light diffusing fiber of claim 1,wherein said core and cladding are structured such that for allviewing-angles from about 30° to about 90° relative to the direction ofpropagation of the light in the light diffusing optical fiber theintensity of the of the emitted radiation does not vary by more than 42%of maximum intensity value.
 11. The light diffusing fiber of claim 2,wherein said nano- to microscale voids or nano or microparticles of saidscattering material are situated and distributed such that for allviewing-angles from about 30° to about 90° relative to the direction ofpropagation of the light in the light diffusing optical fiber theintensity of the emitted radiation does not vary by more than 42% ofmaximum intensity value.
 12. The light diffusing fiber of claim 8,wherein the emitted radiation does not vary by more than about ±21% fromaverage intensity for viewing-angles between 30° and 90°, relative tothe direction of propagation of the light in the light diffusing opticalfiber.
 13. The light diffusing fiber of claim 1, wherein said core andcladding are structured such that for all viewing-angles from about 30°to about 120° relative to the direction of propagation of the light inthe light diffusing optical fiber the intensity of the of the emittedradiation does not vary by more than 45% of maximum intensity value. 14.The light diffusing fiber of claim 2, wherein said nano- to microscalevoids or nano or microparticles of said scattering material are situatedand distributed such that for all viewing-angles from about 30° to about120° relative to the direction of propagation of the light in the lightdiffusing optical fiber the intensity of the emitted radiation does notvary by more than 45% of maximum intensity value.
 15. The lightdiffusing fiber of claim 8, wherein the emitted radiation does not varyby more than about ±22.5% from average intensity for viewing-anglesbetween 30° and 120°, relative to the direction of propagation of thelight in the light diffusing optical fiber.
 16. A light diffusing fibercomprising: a. a core comprising a silica-based glass comprisingscattering defects; and b. a scattering layer surrounding the core, thescattering layer comprising nano- to microscale voids or nano ormicroparticles of a scattering material in a polymer matrix; such thatwhen light is propagating through the light diffusing fiber theintensity of the emitted radiation does not vary by more than about ±38%from average intensity for viewing-angles between 30° and 160°, relativeto the direction of propagation of the light in the light diffusingoptical fiber.
 17. The light diffusing fiber of claim 16, wherein saidcore is a silica based core surrounded by a cladding.
 18. The lightdiffusing fiber of claim 16, wherein a scattering layer surrounds thecore, wherein at least said scattering layer comprises a polymer matrixwith said nano- to microscale voids or nano or microparticles of saidscattering material situated therein.
 19. The light diffusing fiber ofclaim 17, further comprising a cladding surrounding said core, wherein ascattering layer surrounds the core and the cladding, wherein saidscattering layer comprises a polymer matrix with said nano- tomicroscale voids or nano or microparticles of said scattering materialsituated therein.
 20. The light diffusing fiber of claim 18, wherein theslope of the intensity of the emitted radiation to viewing-angle changesby less than 22% within any 20 degree change in viewing-angle forviewing-angles situated between 40° and 90°.
 21. A light diffusing fibercomprising: a. a core and a cladding; and b. nano- to microscale voidsor nano or microparticles of a scattering material, situated anddistributed such that when light is propagating through light diffusingfiber comprising, the intensity of the emitted radiation has maximumintensity, and the maximum intensity value occurs at an angular positionat least 42.5 degrees, relative to the direction of propagation of thelight in the light diffusing optical fiber.
 22. The light diffusingfiber of claim 21, wherein a scattering layer surrounds the core,wherein at least said scattering layer comprises a polymer matrix withsaid nano- to microscale voids or nano or microparticles of saidscattering material situated therein.
 23. The light diffusing fiber ofclaim 22, further comprising a cladding surrounding said core, wherein ascattering layer surrounds the core and the cladding, wherein saidscattering layer comprises a polymer matrix with said nano- tomicroscale voids or nano or microparticles of said scattering materialsituated therein.
 24. The light diffusing fiber of claim 21, wherein thescattering induced attenuation loss comprises from about 0.1 dB/m toabout 50 dB/m at an operating wavelength.
 25. The light diffusing fiberof claim 21, wherein the core comprises a plurality of randomlydistributed voids.
 26. The light diffusing fiber of claim 21, whereinthe cladding comprises a polymer.
 27. The light diffusing fiber of claim21, wherein the microparticles or nanoparticles comprise SiO₂ or Zr. 28.The light diffusing fiber of claim 1, said fiber having substantiallyuniform illumination over its length, wherein said length being in therange of 0.15 to 100 m.
 29. The light diffusing fiber of claim 21, saidfiber having substantially uniform illumination over its length, whereinsaid length being in the range of 0.15 to 100 m.
 30. The light diffusingfiber of claim 1, said fiber having substantially uniform illuminationover its length, said length being in the range of 4-100 m.
 31. Thelight diffusing fiber of claim 21, said fiber having substantiallyuniform illumination over its length, said length being in the range of4-100 m.
 32. The light diffusing fiber of claim 1 said fiber havingscattering induced attenuation loss of about 0.1 dB/m to about 50 dB/mat an operating wavelength.
 33. The light diffusing fiber of claim 1,wherein said light diffusing optical fiber has a length, and the lightdiffusing optical fiber emits light having an intensity along the lengththat does not vary by more than about ±20%.
 34. The light diffusingfiber of claim 21, wherein the light diffusing optical fiber has alength, and emits light having an intensity along the fiber length thatdoes not vary by more than about ±20%.
 35. The light diffusing fiber ofclaim 1, wherein said fiber provides uniform illumination, such that theintensity of light emitted from the light diffusing fiber does not varyby more than 25% over a segment length of 4 to 100 m.
 36. The lightdiffusing fiber of claim 21, wherein said fiber provides uniformillumination, such that the intensity of light emitted from the lightdiffusing fiber does not vary by more than 25% over a segment length of4 to 100 m.
 37. The light diffusing fiber of claim 1, the core having aradius from 10 μm to 600 μm.
 38. The light diffusing fiber of claim 21,the core having a radius from 10 μm to 600 μm.
 39. The light diffusingfiber of claim 1, the core having a radius from 30 μm to 200 μm.
 40. Thelight diffusing fiber of claim 21, the core having a radius from 30 μmto 200 μm.
 41. The light diffusing fiber of claim 37, wherein radialwidth of the cladding is between 10 μm and 100 μm.
 42. The lightdiffusing fiber of claim 38, wherein radial width of the cladding isbetween 10 μm and 100 μm.
 43. The light diffusing fiber of claim 1,wherein the core having a radius from 50 μm to 100 μm and the radialwidth of the cladding is between 10 μm and 100 μm.
 44. The lightdiffusing fiber of claim 21, wherein the core having a radius from 50 μmto 100 μm and the radial width of the cladding is between 10 μm and 100μm